From 9215346d35f4315206131b4ef53138a10429fbde Mon Sep 17 00:00:00 2001
From: Ralf Jung <post@ralfj.de>
Date: Tue, 8 Aug 2023 10:31:42 +0200
Subject: [PATCH] offset_of: guard against invalid use (with unsized fields)

---
 compiler/rustc_target/src/abi/mod.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/compiler/rustc_target/src/abi/mod.rs b/compiler/rustc_target/src/abi/mod.rs
index 084c917cc31..dd435dbb0a3 100644
--- a/compiler/rustc_target/src/abi/mod.rs
+++ b/compiler/rustc_target/src/abi/mod.rs
@@ -39,7 +39,7 @@ fn deref(&self) -> &&'a LayoutS {
 
 /// Trait that needs to be implemented by the higher-level type representation
 /// (e.g. `rustc_middle::ty::Ty`), to provide `rustc_target::abi` functionality.
-pub trait TyAbiInterface<'a, C>: Sized {
+pub trait TyAbiInterface<'a, C>: Sized + std::fmt::Debug {
     fn ty_and_layout_for_variant(
         this: TyAndLayout<'a, Self>,
         cx: &C,
@@ -135,6 +135,11 @@ pub fn offset_of_subfield<C>(self, cx: &C, indices: impl Iterator<Item = usize>)
         for index in indices {
             offset += layout.fields.offset(index);
             layout = layout.field(cx, index);
+            assert!(
+                layout.is_sized(),
+                "offset of unsized field (type {:?}) cannot be computed statically",
+                layout.ty
+            );
         }
 
         offset